Rivet analyses

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/DecayedParticles.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief J/psi -> gamma p pbar
  class BESIII_2012_I1079921 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2012_I1079921);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 443 or Cuts::abspid == 100443);
      declare(ufs, "UFS");
      DecayedParticles PSI(ufs);
      declare(PSI, "PSI");
      declare(Beam(), "Beams");

      // book histos
      ih = -1;
      if (isCompatibleWithSqrtS(3.686, 1e-3))
        ih = 1;
      else if (isCompatibleWithSqrtS(3.1, 1e-3))
        ih = 0;
      raiseBeamErrorIf(ih < 0);
      for (size_t ix = 0; ix < 4; ++ix) {
        book(_h[ix], 1, 1, 1 + ix);
      }
      book(_h[-1], 2, 1, 1);
    }

    // angle cuts due regions of BES calorimeter
    bool vetoPhoton(const double& cTheta) const {
      return cTheta > 0.92 || (cTheta > 0.8 && cTheta < 0.86);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // get the axis, direction of incoming electron
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      Vector3 axis;
      if (beams.first.pid() > 0)
        axis = beams.first.mom().p3().unit();
      else
        axis = beams.second.mom().p3().unit();
      // find the J/psi decays
      static const map<PdgId, unsigned int>& mode = {{2212, 1}, {-2212, 1}, {22, 1}};
      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
      if (PSI.decaying().size() != 1) vetoEvent;
      if (sqrtS() > 3.2 && PSI.decaying()[0].pid() == 443) vetoEvent;
      if (!PSI.modeMatches(0, 3, mode)) vetoEvent;
      const Particle& pp = PSI.decayProducts()[0].at(2212)[0];
      const Particle& pbar = PSI.decayProducts()[0].at(-2212)[0];
      const Particle& gam = PSI.decayProducts()[0].at(22)[0];
      double mass = (pp.mom() + pbar.mom()).mass() - pp.mass() - pbar.mass();
      _h[0 - ih]->fill(mass);
      if (ih > 0 || mass > 0.05) vetoEvent;
      double cTheta = axis.dot(gam.p3().unit());
      // photon angle
      if (vetoPhoton(abs(cTheta))) vetoEvent;
      _h[1]->fill(cTheta);
      // remaining angles
      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(PSI.decaying()[0].mom().betaVec());
      FourMomentum pGamma = boost1.transform(gam.mom());
      FourMomentum pppbar = boost1.transform(pp.mom() + pbar.mom());
      Vector3 e1z = pGamma.p3().unit();
      Vector3 e1y = e1z.cross(axis).unit();
      Vector3 e1x = e1y.cross(e1z).unit();
      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pppbar.betaVec());
      Vector3 axis2 = boost2.transform(boost1.transform(pp.mom())).p3().unit();
      _h[2]->fill(e1z.dot(axis2));
      double phi = atan2(axis2.dot(e1y), axis2.dot(e1x)) / M_PI * 180.;
      _h[3]->fill(phi);
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h, 1.0, false);
    }

    /// @}


    /// @name Histograms
    /// @{
    map<int, Histo1DPtr> _h;
    int ih;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2012_I1079921);

}